...I guess I should know this, but operating when the vehicle is completely turned off, it's safe to say that your transmit power levels should be as low as possible?...On my two meter FM, I notice that I can't transmit 25 watts when the car is off or partially lit up, the rig shuts down...but when started fully, there is no problem....but when operating at the 10 watt level, everything is solid transmit, even when the car is turned off....On my 10 meter rig, I notice that when the car is off, I cant get a signal out, but no problem when on and/or driving.....How much voltage are the rigs starved of when the vehicle is completely turned off???....I thought that the battery should provide a fair amout of voltage, giving the rigs the means to operate at decent power levels???...What do you guys who run 100 watts mobile do when the car is off???...Or you not do any operating at all???....Please explain, so I know what to do when operating my rigs mobile.....by the way, 10 meter mobile has been fun working into EU again....Good suff...

Mobile radios are typically rated for 13.8V input, +/- 15%. So at the low end, the radio is spec'd for 11.75V. When not actively being charged a lead acid battery will have nominally 12.75V and it goes down from there as its' charge depletes.

An SLI battery typically has a pretty low impedance so even assuming a "hefty" draw (20A) the terminal voltage of the battery should only go down a tenth of a volt or so. Most of the drop seen at the DC input of the radio won't usually be the battery, it will be due to wiring. That's why you see a lot of emphasis placed on using large wires and short runs for transceiver power. It doesn't take a lot of wire resistance at high currents to equal tenths or even volts of drop.

If I were you I'd be taking a digital multimeter and measuring the voltage delivered to the power connector at the radio and see if you're dipping below 11.75V during transmit. If not, you have a problem with the rig. If it's dipping below 11.75V, you need to determine why - could be too much or too thin wire, or a bad connection (terminal, fuseholder). Point being, a TX 25W draw (4A-5A@12V) cannot possibly draw a good starting battery down over 1V. If that were the case, you could barely light the lights much less start the car.

I routinely run 100W using storage batteries with no issues. 25W should be a slam dunk.

...On my two meter FM, I notice that I can't transmit 25 watts when the car is off or partially lit up, the rig shuts down...but when started fully, there is no problem....but when operating at the 10 watt level, everything is solid transmit, even when the car is turned off....On my 10 meter rig, I notice that when the car is off, I cant get a signal out, but no problem when on and/or driving.....

To me the situations you have put forward are caused by one of a few things. First, when was the last time you did maintenance on your car battery system? It's true that most modern batteries don't need maintenance, but the connections to them still do. You would be surprised how much voltage can be lost by having just one loose battery connection.

Then there is the question of how new the battery is. Does it have enough power in it to really turn the engine over, or is it barely able to spin the engine enough to get it started? The battery may be on its last legs, and the low voltage you notice when operating may be a harbinger of things to come--having to call someone to get your car started (jumped) one of these days, now that cold weather is coming.

Lastly, there is the question of the wiring connections from the rigs to your battery. Are your rigs direct wired, or are you using power from the car wiring harnesses or fuse block? Take the time to wire directly to the battery instead of connections in the car--not doing that is where the majority of voltage drop issues come from. Make sure those wires are at least twelve gauge--ten gauge is better. Make sure each and every connection is tight and corrosion free, even the fuse clips and the harness to rig plugs.

If you take the time and put in the effort--and possibly the cost of a new battery, you shouldn't have any problem with your rigs if your car is switched off and you want to use them. 73!

I think Mark has given you the key, here. I'd definitely check the car battery (is it still good?) and the power wiring from the battery to the radio. It happens regularly that I listen on HF for 45-60 minutes, transmitting occasionally (working a little DX while my wife is shopping), with my car engine not running, and I've never had a problem with that.

The battery was installed two summers ago, and the direct line to the battery was installed last summer....I will take a look at the battery and see, but I am sure it's OK....I have a hunch as to what the problem might be.....I am going to take a look at the power chord connection to see if I can tighten it up a bit....Thanks for the tid bits guys...

The battery was installed two summers ago, and the direct line to the battery was installed last summer....I will take a look at the battery and see, but I am sure it's OK....I have a hunch as to what the problem might be.....I am going to take a look at the power chord connection to see if I can tighten it up a bit....Thanks for the tid bits guys...

VKA3NRX

Any Battery irrespective of new or old, when run down below 10.5 VOLTS are considered toast.

>>> " any nominal 12 volt lead acid battery is considered discharged when the voltage drops to 10.5 volts under load. Discharging them lower than this will drastically reduce the life of the battery" <<< end of quote.

This leads me to ask the question of you. How many times have you discharged the Battery below 10.5 Volt while using the radio?

I would strongly discourage running your Radio off the Vehicle's Battery without the engine/Alternator running.Especially at 100 watts PEP.BTW, loose connections (DC Current) are HELL on Batteries under a Load.

...Any Battery irrespective of new or old, when run down below 10.5 VOLTS are considered toast....

No, not necessarily. If the battery is continually discharged beyond that point, then yes, but one or two times? No. Batteries can 'bounce back' if they're discharged beyond that once or twice, but it takes a good, long charge to do it. If you keep discharging the battery to that point, though, I agree that sooner than later the battery will be no good.

Appropriate troubleshooting techniques would include taking some DC voltage readings at various points in the system starting with the voltage directly across the battery with the transmitter keyed and the engine off. A good, fully charged, car battery should power a 100W radio at full output for a couple of hours (depending on duty cycle) with no problem. I operate at the 100W level routinely from my vehicle, often with the engine off.

If your car always starts okay then I expect the voltage drop is occuring in the radio wiring/connections.

Appropriate troubleshooting techniques would include taking some DC voltage readings at various points in the system starting with the voltage directly across the battery with the transmitter keyed and the engine off. A good, fully charged, car battery should power a 100W radio at full output for a couple of hours (depending on duty cycle) with no problem. I operate at the 100W level routinely from my vehicle, often with the engine off.

If your car always starts okay then I expect the voltage drop is occuring in the radio wiring/connections.

>>> the voltage drop is occuring in the radio wiring/connections. <<<

Where else does "Voltage Drop" usually occurs?

>>> A good, fully charged, car battery should power a 100W radio at full output for a couple of hours (depending on duty cycle) with no problem. <<<

I shudder at the thought of the MASSIVE amount of IMD that is being broadcast on the frequency running 100 watts from the battery of Car for several hours without the Engine running!

There is no standard individual car battery that will "Independently" sustain over 20 Amps for several hours to maintain 100 watts. NONE!!!! BTW. Please do not tell me a 20AH, or better yet a 100AH battery is capable of such a feat.

I shudder at the thought of the MASSIVE amount of IMD that is being broadcast on the frequency running 100 watts from the battery of Car for several hours without the Engine running!

There is no standard individual car battery that will "Independently" sustain over 20 Amps for several hours to maintain 100 watts. NONE!!!! BTW. Please do not tell me a 20AH, or better yet a 100AH battery is capable of such a feat.

And why not? It depends on the way the station is being run. Intermittent 20 amp draw with a duty cycle of 5 to 10 percent will not draw the average automotive battery down that much. Your supposition of 20 amps being sustained over several hours is hogwash, and you know it. No ham will continuously transmit several hours in that manner, and you know that too!

Most rigs will simply switch off when the voltage level drops below their speced operating level, and most hams who do mobile ops know enough to start their car if they're going to be using the transmitter of their rigs for an extended period. 73!

I shudder at the thought of the MASSIVE amount of IMD that is being broadcast on the frequency running 100 watts from the battery of Car for several hours without the Engine running!

There is no standard individual car battery that will "Independently" sustain over 20 Amps for several hours to maintain 100 watts. NONE!!!! BTW. Please do not tell me a 20AH, or better yet a 100AH battery is capable of such a feat.

And why not? It depends on the way the station is being run. Intermittent 20 amp draw with a duty cycle of 5 to 10 percent will not draw the average automotive battery down that much. Your supposition of 20 amps being sustained over several hours is hogwash, and you know it. No ham will continuously transmit several hours in that manner, and you know that too!

Most rigs will simply switch off when the voltage level drops below their speced operating level, and most hams who do mobile ops know enough to start their car if they're going to be using the transmitter of their rigs for an extended period. 73!

Operating a Mobile radio (12 volts) at 100 watts tantamounts to 100% duty cycle.He did say 100 watts which is the equivalent of 100% duty cycle for several hours.

There is no standard individual car battery that will "Independently" sustain over 20 Amps for several hours to maintain 100 watts. NONE!!!! BTW. Please do not tell me a 20AH, or better yet a 100AH battery is capable of such a feat.

Milverton, I suspect what he's talking about is the same sort of thing I do when my wife is in a store, and I'm outside in the parking lot. I'll listen, tune around the bands, and every few minutes I might work a station. I don't think he's talking about *transmitting* for any great length of time--nobody really does that, except maybe that moron on 14.313. :-) I do that--listen for 10-15 minutes, work a station, listen again--I do that for an hour at a time with the engine off, no problem.

As long as the battery is good and holds a charge at the proper level, the radio should work fine whether the engine is on or off. As some of the other stated check every connection including the fuse holders (you do have these installed?) between the battery and radio. I have one fuse holder (located in the engine compartment) that rusted to the point where the voltage read between 12.5 and 13.5 no loaded (radio turned off), but dropped to 9 volts when transmitting (radio did shut off). Replace the fuse holder with an automotive 30 amp circuit breaker and so far no issues.

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